Because the IRS announced it considers bitcoin property, not a currency, most people who buy and sell bitcoin will face the same taxes they would if they were trading stocks. Those who use it to make purchases could realize a taxable gain or loss on every transaction.

"In general, the sale or exchange of convertible virtual currency, or the use of convertible virtual currency to pay for goods or services in a real-world economy transaction, has tax consequences that may result in a tax liability," the IRS said in guidance published Tuesday.

Suppose you buy a bitcoin for $500. Its value rises to $800, and you use it to purchase $800 worth of sheets and blankets on Overstock.com. The difference - $300 - would be a capital gain. If you held the bitcoin for one year or less, it would be taxed as a short-term gain, at the same rate that applies to ordinary income from a job or self-employment. If you held it for more than one year, it would be taxed at the lower long-term capital gains rate.

Retailers and the IRS

Overstock.com, which in January became the first major U.S. retailer to accept the crypto-currency, would recognize $800 worth of sales, just as it would if the transaction took place in dollars. A merchant selling its own inventory would not be required to send you or the IRS a Form 1099 reporting the transaction, although it still could be traceable, says Lee Sheppard, a contributing editor with Tax Notes.

If, when you sell your bitcoin or use it to make a purchase, it is worth less than you paid, you would recognize a loss, which can be used to offset gains. When you file your taxes, you net out all capital gains and losses to determine if you have a net long-term or short-term gain or loss.

This process would apply to all bitcoin transactions, no matter how small.

"For people using (bitcoin) as a means to pay for something, it would be a capital asset in those hands," and treated as such, says Mark Luscombe, principal analyst with CCH Tax and Accounting.

For people who are deemed to be traders or dealers in bitcoin, any profits generally would be treated as ordinary income. Likewise, people who create new bitcoins through a process known as mining would pay ordinary income tax on the fair market value of the bitcoin at the time it is received.

Although some were hoping the IRS would deem it a currency, the decision to treat bitcoin as property was not unexpected.

"Anyone who thought it had some special status as currency, the IRS is trying to disabuse them of that notion," Luscombe says. "If you hold dollars and they change in value over the course of time, that appreciation is not taxable," he says. If you hold stock or bitcoin and it appreciates, "that is taxable."

The IRS also made it clear that if an employer pays an employee in bitcoin, it will be treated as wages for employment tax purposes. It will not, however, treat bitcoin as a currency that could generate foreign currency gains or losses.

2013 tax returns

People who had bitcoin transactions last year should consider the new guidance in preparing their 2013 returns.

The IRS notes that bitcoin users could be subject to penalties if they did not treat bitcoin transactions that took place before Tuesday in accordance with its new guidance. However, "penalty relief may be available to taxpayers" who can prove that their failure to comply with the new rules "is due to reasonable cause."

Sheppard notes, "If you were doing this for tax evasion, you don't get penalty relief."

Angel, the Wharton professor, said the complexity of the new rules could discourage smaller merchants from accepting bitcoin.

"If I am Jim's muffin shop, and I am already up to my eyeballs in accounting fees, I would be thinking I will wait until I see a real good business reason to do this," he says. Today, "most merchants accept it as a novelty statement to attract attention or (want to be perceived) as hipsters or are part of a pro-freedom group."

It's unclear how much companies in bitcoin services will help customers in complying with the new rules.

Coinbase, a San Francisco company that provides digital wallets where users can store their bitcoins, said customers can view their transaction history in bitcoins and dollars. But it declined to discuss the new rules beyond the following statement: "The IRS ruling provides clarity and validation which enables bitcoin to be accessible to the masses. Coinbase is prepared to help consumers and merchants meet the guidelines."

In a blog post, the Bitcoin Foundation said it "appreciates the IRS' hard work in providing much-needed clarity to those transacting in digital currencies. ... However, tax treatment of Bitcoin as a property, and not a currency, may make compliance with tax laws unnecessarily cumbersome and imposes untenable recording and reporting requirements on its users."

Gains and losses

It added: "The tax laws currently permit individuals to ignore small gains and losses in foreign currencies. Similar treatment for digital currencies would harmonize the law with the way most people actually use digital currencies. Artificially characterizing this use case as a transaction in property would make one of the most innovative features of this technology hard to use for those who wish to be compliant."

Patrick Byrne, chief executive of Overstock.com, says his company takes in about 200 bitcoins per week from customers, which at the current exchange rate equals about $120,000. Initially, Overstock immediately converted all bitcoin into dollars, but in February it started holding on to 10 percent "because one day we might start paying vendors in bitcoin," he said.

He said the IRS ruling will affect that 10 percent, but the additional accounting won't dissuade him from accepting bitcoins.

And Byrne isn't sure whether the decision will discourage customers from paying with the crypto-currency. Some people bought bitcoin at prices much higher than current rates, meaning for them, "using it at Overstock is a way of realizing a capital loss," he said.